Sub-Saturn Planet Candidates to HD 16141 and HD 46375

Precision Doppler measurements from the Keck/HIRES spectrometer reveal periodic Keplerian velocity variations in the stars HD 16141 and HD 46375. HD 16141 (G5 IV) has a period of 75.8 d and a velocity amplitude of 11 m/s, yielding a companion having Msini = 0.22 Mjup and a semimajor axis, a = 0.35 AU. HD 46375 (K1 IV/V) has a period of 3.024 d and a velocity amplitude of 35 m/s, yielding a companion with Msini=0.25 Mjup, a semimajor axis of a = 0.041 AU, and an eccentricity of 0.04 (consistent with zero). These companions contribute to the rising planet mass function toward lower masses.Comment: 4 Figure

Ten Low Mass Companions from the Keck Precision Velocity Survey

Ten new low mass companions have emerged from the Keck precision Doppler velocity survey, with minimum (msini) masses ranging from 0.8 mjup to 0.34 msun. Five of these are planet candidates with msini < 12 mjup, two are brown dwarf candidates with msini ~30 mjup, and three are low mass stellar companions. Hipparcos astrometry reveals the orbital inclinations and masses for three of the (more massive) companions, and it provides upper limits to the masses for the rest. A new class of extrasolar planet is emerging, characterized by nearly circular orbits and orbital radii greater than 1 AU. The planet HD 4208b appears to be a member of this new class. The mass distribution of extrasolar planets continues to exhibit a rapid rise from 10 mjup toward the lowest detectable masses near 1 msat.Comment: 26 pages, TeX, plus 13 postscript figure

On the Radii of Close-in Giant Planets

The recent discovery that the close-in extrasolar giant planet, HD209458b, transits its star has provided a first-of-its-kind measurement of the planet's radius and mass. In addition, there is a provocative detection of the light reflected off of the giant planet, $\tau$ Boo b. Including the effects of stellar irradiation, we estimate the general behavior of radius/age trajectories for such planets and interpret the large measured radii of HD209458b and $\tau$ Boo b in that context. We find that HD209458b must be a hydrogen-rich gas giant. Furthermore, the large radius of close-in gas giant is not due to the thermal expansion of its atmosphere, but to the high residual entropy that remains throughout its bulk by dint of its early proximity to a luminous primary. The large stellar flux does not inflate the planet, but retards its otherwise inexorable contraction from a more extended configuration at birth. This implies either that such a planet was formed near its current orbital distance or that it migrated in from larger distances ($\geq$0.5 A.U.), no later than a few times $10^7$ years of birth.Comment: aasms4 LaTeX, 1 figure, accepted to Ap.J. Letter

The F-GAMMA program: Multi-frequency study of Active Galactic Nuclei in the Fermi era. Program description and the first 2.5 years of monitoring

To fully exploit the scientific potential of the Fermi mission, we initiated the F-GAMMA program. Between 2007 and 2015 it was the prime provider of complementary multi-frequency monitoring in the radio regime. We quantify the radio variability of gamma-ray blazars. We investigate its dependence on source class and examine whether the radio variability is related to the gamma-ray loudness. Finally, we assess the validity of a putative correlation between the two bands. The F-GAMMA monitored monthly a sample of about 60 sources at up to twelve radio frequencies between 2.64 and 228.39 GHz. We perform a time series analysis on the first 2.5-year dataset to obtain variability parameters. A maximum likelihood analysis is used to assess the significance of a correlation between radio and gamma-ray fluxes. We present light curves and spectra (coherent within ten days) obtained with the Effelsberg 100-m and IRAM 30-m telescopes. All sources are variable across all frequency bands with amplitudes increasing with frequency up to rest frame frequencies of around 60 - 80 GHz as expected by shock-in-jet models. Compared to FSRQs, BL Lacs show systematically lower variability amplitudes, brightness temperatures and Doppler factors at lower frequencies, while the difference vanishes towards higher ones. The time scales appear similar for the two classes. The distribution of spectral indices appears flatter or more inverted at higher frequencies for BL Lacs. Evolving synchrotron self-absorbed components can naturally account for the observed spectral variability. We find that the Fermi-detected sources show larger variability amplitudes as well as brightness temperatures and Doppler factors, than non-detected ones. Flux densities at 86.2 and 142.3 GHz correlate with 1 GeV fluxes at a significance level better than 3sigma, implying that gamma rays are produced very close to the mm-band emission region.Comment: Accepted for publication in section 4. Extragalactic astronomy of Astronomy and Astrophysics (18 pages, 9 figures

Filling in the Gaps in the 4.85 GHz Sky

We describe a 4.85 GHz survey of bright, flat-spectrum radio sources conducted with the Effelsberg 100 m telescope in an attempt to improve the completeness of existing surveys, such as CRATES. We report the results of these observations and of follow-up 8.4 GHz observations with the VLA of a subset of the sample. We comment on the connection to the WMAP point source catalog and on the survey's effectiveness at supplementing the CRATES sky coverage.Comment: 13 pages, 3 figures, 2 tables. Accepted for publication in the Astronomical Journal. Tables available in electronic form: http://astro.stanford.edu/gaps

Young Globular Clusters and Dwarf Spheroidals

Most of the globular clusters in the main body of the Galactic halo were formed almost simultaneously. However, globular cluster formation in dwarf spheroidal galaxies appears to have extended over a significant fraction of a Hubble time. This suggests that the factors which suppressed late-time formation of globulars in the main body of the Galactic halo were not operative in dwarf spheroidal galaxies. Possibly the presence of significant numbers of ``young'' globulars at R_{GC} > 15 kpc can be accounted for by the assumption that many of these objects were formed in Sagittarius-like (but not Fornax-like) dwarf spheroidal galaxies, that were subsequently destroyed by Galactic tidal forces. It would be of interest to search for low-luminosity remnants of parental dwarf spheroidals around the ``young'' globulars Eridanus, Palomar 1, 3, 14, and Terzan 7. Furthermore multi-color photometry could be used to search for the remnants of the super-associations, within which outer halo globular clusters originally formed. Such envelopes are expected to have been tidally stripped from globulars in the inner halo.Comment: 18 pages, with 2 figures, in LaTeX format; to appear in the Astrophysical Journal in February 200

15 GHz Monitoring of Gamma-ray Blazars with the OVRO 40 Meter Telescope in Support of Fermi

We present results from the first two years of our fast-cadence 15 GHz gamma-ray blazar monitoring program, part of the F-GAMMA radio monitoring project. Our sample includes the 1158 blazars north of -20 degrees declination from the Candidate Gamma-Ray Blazar Survey (CGRaBS), which encompasses a significant fraction of the extragalactic sources detected by the Fermi Gamma-ray Space Telescope. We introduce a novel likelihood analysis for computing a time series variability amplitude statistic that separates intrinsic variability from measurement noise and produces a quantitative error estimate. We use this method to characterize our radio light curves. We also present results indicating a statistically significant correlation between simultaneous average 15 GHz radio flux density and gamma-ray photon flux.Comment: 5 pages, 7 figures; 2009 Fermi Symposium; eConf Proceedings C09112

Detailed Analysis of Nearby Bulgelike Dwarf Stars III. Alpha and Heavy-element abundances

The present sample of nearby bulgelike dwarf stars has kinematics and metallicities characteristic of a probable inner disk or bulge origin. Ages derived by using isochrones give 10-11 Gyr for these stars and metallicities are in the range -0.80< [Fe/H]< +0.40. We calculate stellar parameters from spectroscopic data, and chemical abundances of Mg, Si, Ca, Ti, La, Ba, Y, Zr and Eu are derived by using spectrum synthesis. We found that [alpha-elements/Fe] show different patterns depending on the element. Si, Ca and Ti-to-iron ratios decline smoothly for increasing metallicities, and follow essentially the disk pattern. O and Mg, products of massive supernovae, and also the r-process element Eu, are overabundant relative to disk stars, showing a steeper decline for metallicities [Fe/H] > -0.3 dex. [s-elements/Fe] roughly track the solar values with no apparent trend with metallicity for [Fe/H] < 0, showing subsolar values for the metal rich stars. Both kinematical and chemical properties of the bulgelike stars indicate a distinct identity of this population when compared to disk stars.Comment: 21 pages, 9 figures, to appear in Ap

Metallicity in the Galactic Center: The Arches cluster

We present a quantitative spectral analysis of five very massive stars in the Arches cluster, located near the Galactic center, to determine stellar parameters, stellar wind properties and, most importantly, metallicity content. The analysis uses a new technique, presented here for the first time, and uses line-blanketed NLTE wind/atmosphere models fit to high-resolution near-infrared spectra of late-type nitrogen-rich Wolf-Rayet stars and OfI+ stars in the cluster. It relies on the fact that massive stars reach a maximum nitrogen abundance that is related to initial metallicity when they are in the WNL phase. We determine the present-day nitrogen abundance of the WNL stars in the Arches cluster to be 1.6% (mass fraction) and constrain the stellar metallicity in the cluster to be solar. This result is invariant to assumptions about the mass-luminosity relationship, the mass-loss rates, and rotation speeds. In addition, from this analysis, we find the age of the Arches cluster to be 2-2.5Myr, assuming coeval formation

A Planet at 5 AU Around 55 Cancri

We report precise Doppler shift measurements of 55 Cancri (G8V) obtained from 1989 to 2002 at Lick Observatory. The velocities reveal evidence for an outer planetary companion to 55 Cancri orbiting at 5.5 AU. The velocities also confirm a second, inner planet at 0.11 AU. The outer planet is the first extrasolar planet found that orbits near or beyond the orbit of Jupiter. It was drawn from a sample of ~50 stars observed with sufficient duration and quality to detect a giant planet at 5 AU, implying that such planets are not rare. The properties of this jupiter analog may be compared directly to those of the Jovian planets in our Solar System. Its eccentricity is modest, e=0.16, compared with e=0.05 for both Jupiter and Saturn. Its mass is at least 4.0 jupiter masses (M sin i). The two planets do not perturb each other significantly. Moreover, a third planet of sub-Jupiter mass could easily survive in between these two known planets. Indeed a third periodicity remains in the velocity measurements with P = 44.3 d and a semi-amplitude of 13 m/s. This periodicity is caused either by a third planet at a=0.24 AU or by inhomogeneities on the stellar surface that rotates with period 42 d. The planet interpretation is more likely, as the stellar surface is quiet, exhibiting log(R'_{HK}) = -5.0 and brightness variations less than 1 millimag, and any hypothetical surface inhomogeneity would have to persist in longitude for 14 yr. Even with all three planets, an additional planet of terrestrial--mass could orbit stably at ~1 AU. The star 55 Cancri is apparently a normal, middle-aged main sequence star with a mass of 0.95 solar masses, rich in heavy elements ([Fe/H] = +0.27). This high metallicity raises the issue of the relationship between its age, rotation, and chromosphere.Comment: 47 pages, 4 tables, 12 figures, uses AASTE